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A white-winged crossbill (female, probably an adult) perches where the birds are most commonly encountered, near the cone-bearing top of a spruce tree. Keith Corliss/Forum Communications Co.

Odd bill keeps bird searching for food

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Every once in a while, a keen observer will spot an obvious flaw in the seemingly error-free world of bird morphology. Maybe it's a missing toe or eye. Sometimes it's a feather colored differently than the rest or a wing that can no longer support flight. The sources of such deviations can either come from within the bird, such as a hormonal imbalance causing errant color pigmentation. Or it can be external, like a tailless bird having barely escaped the lunge of a neighborhood cat.

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In any case, the consequences of being physically compromised in the rough-and-tumble natural world are often harsh. Less than robust actors are usually removed rather quickly from the scene by opportunistic predators. That's the main reason we don't see them very often, the individuals are being deleted with cold efficiency.

Yet there are two species of North American finch that conduct productive lives sporting the strangest of adaptations to their beaks; the ends of which are quite obviously misaligned, or crossed. Without knowing better, a casual observer might deem these rather curious looking birds malformed. Understand the food sources of red crossbills (Loxia curvirostra) and white-winged crossbills (Loxia leucoptera), however, and it becomes apparent that, far from feeling pity, admirers should be applauding the striking characteristic for its unique ingenuity.

The birds feed on cones, or more accurately, the seeds held within the cones of evergreen trees. Leaving aside the complexity of red crossbills for another day, white-winged crossbills feed nearly exclusively on the seeds of various spruce trees and somewhat on tamarac. Their bills function by prying open the scales of closed cones exposing the embedded seeds, which are then extracted by the bird's tongue. To know the extreme unpredictability in cone production is to know the life history of white-winged crossbills.

Under normal (if that word even applies to white-wings) circumstances, the birds are restless residents of Canadian boreal forests, reaching into the border states (like northern Minnesota) and the Rocky Mountains as far south as Wyoming and Colorado. Wandering, though, is the species' claim to fame. White-winged crossbills are constantly searching for cones and can cover vast distances in their nomadic quest for food.

Uncommonly, this bird is found outside of its normal forested range. Rarer still is something called an irruption, when considerable numbers of the birds roam south into normally crossbill-free areas. Such is the case this fall. Reports of white-winged crossbills continue to pile up from all across North Dakota and Minnesota.

The reason for these wanderings is open to debate. I tend to prefer the two-pronged answer which combines a successful breeding season (thus more "mouths" to feed) with a crash in cone production in the boreal forest.

Once seen well, white-winged crossbills are not to be confused with any other bird. About the size of house sparrows, males are pinkish red overall with two white wing bars set on black wings. Females and immatures appear yellow-green on a gray base color, still sporting the wing bars. The heads of the birds appear large, their bills even larger.

Seeing these birds is not altogether easy though. Since they spend most of their time gleaning seeds from spruce cones, the birds are typically high in the trees where they can remain frustratingly hidden for extended periods of time. While feeding, they can remain quite silent too.

Two clues might help the prospective viewer find these wandering nomads. One is the presence of flaky seed husks falling from the sky. There is only one reason for the papery brown stuff to be floating on the air: something is eating the seeds.

The second giveaway is their voice. For some reason white-winged crossbills become very loud and vocal just prior to departing a feeding area. Entire groups then lift off from trees and continue chattering until a different suitable site is found. You might even catch a group on the ground where they will infrequently drink from a water puddle or feed on fallen cones.

This certainly appears to be the moment to add white-winged crossbill to your state bird list or perhaps even your life list. Opportunities like this might not come around again for many years.

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